1. Field of the Invention
The present invention relates to an image capturing apparatus and a control method and, particularly, to an exposure control technique in an image capturing apparatus.
2. Description of the Related Art
In an image capturing apparatus such as a digital camera, exposure control is performed to change the exposure settings at the time of image capturing in accordance with the brightness of a subject. More specifically, in, for example, landscape image capturing during the daytime in which an overall subject is bright, the sensitivity of an image sensor is set low, the shutter speed is set high (the exposure time is set short), and the aperture value is set large. Also, in, for example, night scene image capturing in which an overall subject is dark, the sensitivity of an image sensor is set high, the shutter speed is set low (the exposure time is set long), and the aperture value is set small.
In image capturing under the condition in which the shutter speed is set relatively low (the exposure time is set relatively long), as in a night scene, it is desired to use a tripod to obtain a satisfactory image capturing result. This is because, for example, the exposure time at the time of night scene image capturing is longer than that required in the daytime. That is, during a long exposure time, a displacement of an optical image formed on an image sensor occurs due, for example, to a camera shake of a photographer who grips an image capturing apparatus, so the sharpness of the image capturing result is lost.
To solve this problem, Japanese Patent No. 4046836 discloses an image capturing apparatus which sets an image capturing mode suitable for image capturing using a tripod when it is determined that the image capturing apparatus is fixed on, for example, a tripod and does not vibrate, based on the detection result of vibration (shake) of the image capturing apparatus.
When the image capturing apparatus is, for example, an exchangeable lens type digital camera, the shake detection method changes depending on whether an exchangeable lens includes a shake sensor which detects a camera shake, such as a gyro. That is, when the exchangeable lens includes no shake sensor, a camera shake can be detected by detecting, as a motion vector, a displacement of an optical image formed on an image sensor as the apparatus vibrates.
However, a method of detecting a shake using a motion vector has a reliability lower than that of a method of detecting a shake using a sensor which detects a shake. This is because it is difficult to, for example, discriminate between a subject motion and a camera motion (camera shake), and isolate them from each other.
Therefore, the exposure settings are preferably changed between the case wherein a shake is detected using a motion vector and that wherein a shake is detected using a sensor.